The present invention relates to an extractor grid for an electron source used in a display device and more particularly to an electron source for use in a matrix addressed electron beam display.
Electron sources are particularly, although not exclusively, useful in display applications, especially flat panel display applications. Such applications include television receivers and visual display units for computers, especially, although not exclusively, portable computers, personal organizers, communications equipment, and the like.
U.S. patent application Ser. No. 08/695,856, filed on Aug. 9, 1996 now U.S. Pat. No 5,917,277, which corresponds to UK Patent Application No. 2304981, assigned to the assignee of the instant Patent Application and the disclosure of which is incorporated herein by reference, discloses a magnetic matrix display having as an electron source a cathode for emitting electrons, a permanent magnet with a two dimensional array of channels extending between opposite poles of the magnet, the direction of magnetization being from the surface facing the cathode to the opposing surface. The magnet generates, in each channel, a magnetic field for forming electrons from the cathode means into an electron beam. The display also has a screen for receiving an electron beam from each channel. The screen has a phosphor coating facing the side of the magnet remote from the cathode, the phosphor coating comprising a plurality of stripes per column, each stripe corresponding to a different channel. Flat panel display devices based on a magnetic matrix will hereinafter be referred to as MMD or Magnetic Matrix Display.
A remote virtual cathode system used as the cathode in a Magnetic Matrix Display employs a mesh or grid in the vicinity of the physical cathode (the source of electrons) to extract electrons from the local virtual cathode (the space charge cloud in front of the physical cathode) by means of a positive potential on the grid with respect to the physical cathode potential. The virtual cathode potential is slightly below that of the physical cathode potential by virtue of the presence of a substantial number of negatively charged electronsxe2x80x94the space charge cloudxe2x80x94and the virtual cathode is typically a few tens of micrometers in front of the physical cathode.
Child""s Law       j    e    =      4    ⁢          xe2x80x83        ⁢                  ε        0            9        ⁢                  2        ⁢                  xe2x80x83                ⁢                                            Z              q                                      m              0                                ·                                    V              0                              3                2                                                    d              2                                          
j=current density
Z is the charge on the particle
V is the accelerating voltage
m is the rest mass of the particle
d is the accelerating gap
Child""s Law is an empirically determined relationship which, amongst other things, relates current density, extraction voltage and distance between the extraction grid and the physical cathode. Note that Child""s Law is a one-dimensional model only. Changes in distance between the extractor grid and electron source will result in changes in the current density which can be extracted from the virtual cathode, hence resulting in a luminance non-uniformity in a display employing such a system.
A second issue that must be addressed in a remote virtual cathode is the efficiency of the system. Some electrons will collide with the extractor grid. The percentage that do so may be found, to a first approximation, by the xe2x80x9caperture ratioxe2x80x9d of the grid. If, for example, the grid is formed by 10 xcexcm wide wires on 250 xcexcm centers, the ratio of xe2x80x9copenxe2x80x9d area to the total area is 2402/2502=92.16 percent. In other words, 7.84 percent of the extracted electrons will collide with the grid after leaving the virtual cathode and will not contribute to the remote virtual cathode.
The preferred remote virtual cathode system operates by allowing the electrons to continually oscillate through the extractor grid. The extractor grid is at a positive potential with respect to the physical cathode and remote virtual cathode. Each time an individual electron passes through the extractor grid, it has, for the example square mesh grid above, a 7.84 percent chance of colliding with the grid and being xe2x80x9clostxe2x80x9d.
Therefore, it is most desirable that the extractor grid have the maximum possible transmission to retain high efficiency.
A third effect that may manifest itself in a remote virtual cathode system is interaction between the X-Y aperture structure of the pixels in the display and the X-Y structure of the extractor grid. If the two are closely (but not perfectly) aligned, an effect akin to Moire fringing may occur. This will lead to luminance uniformity problems over the display area.
For successful implementation of a remote virtual cathode system the following problems must be solved:
1. Maintaining a constant distance between the electron source and the extractor grid. This, coupled with a constant extraction voltage will ensure extraction current density consistent with the emission properties of the cathode. (It will not compensate for emission non-uniformities on the physical cathode surface which may be attenuated by equalization of the local virtual cathode potential due to space charge effects therein.)
2. Providing the extractor grid with sufficient aperture ratio to achieve the desired efficiency.
3. Ensuring that there are no interference effects between the pixel array structure and the extractor grid.
Therefore, one purpose of this invention is to have an extractor grid for an electron source used in a display device, and more particularly to an electron source for use in a matrix addressed electron beam display.
Another purpose of this invention is to have the electron source further comprising a permanent magnet perforated by a plurality of channels extending between opposite poles of the magnet wherein each channel forms electrons received from the cathode means into an electron beam for guidance towards a target.
Still another purpose of this invention is to have at least one aperture in the extractor grid correspond to at least one of the plurality of channels in the permanent magnet.
Yet another purpose of this invention is to have each one of the plurality of apertures in the extractor grid correspond to a plurality of the plurality of channels in the permanent magnet.
Still yet another purpose of the invention is to have the extractor grid further comprise a frame positioned at the periphery of the extractor grid and the extractor grid is located on the frame by means of a plurality of insulating members.
Yet another purpose of the invention is that the spacing member further comprise at least one dielectric layer or metal oxide layer which substantially covers the spacing member.
Therefore, in one aspect this invention comprises an electron source comprising at least one cathode means, and at least one extractor grid used to extract electrons from said cathode means, said extractor grid being a substantially planar sheet having at least one aperture in said sheet and having at least one spacing member for spacing said extractor grid at a constant, predetermined spacing from said cathode, said spacing member being formed by removing material around a substantial portion of said periphery of said aperture and folding a remaining portion of said periphery of said aperture at substantially a right angle to said planar sheet.
In another aspect this invention comprises a display device comprising:
an electron source comprising:
cathode means, and an extractor grid used to extract electrons from said cathode means, said extractor grid being a substantially planar sheet having a plurality of apertures in said sheet and having a plurality of spacing members for spacing said extractor grid at a constant, predetermined spacing from said cathode means, each of said spacing members being formed by removing material around a substantial portion of said periphery of said apertures form at least one flap, and folding at least a portion of said periphery of said flap at substantially a right angle to said planar sheet,
a permanent magnet perforated by a plurality of channels extending between opposite poles of said magnet wherein each channel forms electrons received from said cathode means into an electron beam for guidance towards a target;
a screen for receiving electrons from said electron source, said screen having a phosphor coating facing said side of said magnet remote from said electron source;
grid electrode means disposed between said electron source and said magnet for controlling flow of electrons from said electron source into each channel;
anode means disposed on said surface of said magnet remote from said electron source for accelerating electrons through said channels; and
means for supplying control signals to said grid electrode means and said anode means to selectively control flow of electrons from said electron source to said phosphor coating via said channels thereby to produce an image on said screen.
In yet another aspect this invention comprises a computer system comprising: memory means; data transfer means for transferring data to and from said memory means; processor means for processing data stored in said memory means; and a display device for displaying data processed by said processor means, said display device comprising:
an electron source comprising:
at least one cathode means, and at least one extractor grid used to extract electrons from said cathode means, said extractor grid being a substantially planar sheet having at least one aperture in said sheet and having at least one spacing member for spacing said extractor grid at a constant, predetermined spacing from said cathode means, each of said spacing member being formed by removing material around a substantial portion of said periphery of said aperture and folding a remaining portion of said periphery of said aperture at substantially a right angle to said planar material, a permanent magnet perforated by at least one channel extending between opposite poles of said magnet wherein each channel forms electrons received from said cathode means into an electron beam for guidance towards a target;
a screen for receiving electrons from said electron source, said screen having a phosphor coating facing said side of said magnet remote from said electron source;
grid electrode means disposed between said electron source and said magnet for controlling flow of electrons from said electron source into each channel;
anode means disposed on said surface of said magnet remote from said electron source for accelerating electrons through said channel; and
means for supplying control signals to said grid electrode means and said anode means to selectively control flow of electrons from said electron source to said phosphor coating via said channels thereby to produce an image on said screen.